Question

已知:9+√13与9-√13的小数部分分别是a和b,求代数式4a+4b的值

Answer 1

3 < √13 < 4

所以

12 < 9 + √13 < 13

5 < 9 - √13 < 6

所以

a = 9 + √13 - 12 = √13 - 3

b = 9 - √13 - 5 = 4 - √13

所以

4a + 4b

= 4(a + b)

= 4(√13 - 3 + 4 - √13)

= 4×1

= 4